Geophysical methods for landfill characterization · 2020. 10. 28. · RAWFILL Geophysical methods...
Transcript of Geophysical methods for landfill characterization · 2020. 10. 28. · RAWFILL Geophysical methods...
RAWFILL
Geophysical methods for landfill
characterizationDavid Caterina2, Ben Dashwood1, Itzel Isunza Manrique2, Arnaud Watlet1, Cornelia M. Inauen1
1 British Geological Survey, Nottingham, UK, 2 University of Liege, Urban and Environmental Engineering, Belgium
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“The subsurface site characterization of the geology, geological
structure, groundwater, contamination, and human artifacts beneath the
Earth's surface, based on the lateral and vertical mapping of physical
property variations that are remotely sensed using non-invasive
technologies” (EEGS 2018)
INTRODUCTION
A short introduction to geophysics
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INTRODUCTION
Why geophysics for landfill characterization?
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Accurate information
BUT
Good spatial characterization
can be costly and lead to higher
cross-contamination risks
INTRIDUCTION
Traditional approach:
drilling – sampling - analysis
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Medical analogy
Combine geophysics with traditional techniques
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RAWFILL approach
How?
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Stainless steel electrodesExample: using electrical resistivity
tomography (ERT) & induced polarization (IP)
Principle 1:combine complementary geophysical methods and plan
the geophysical survey based on a-priory site
information
RAWFILL approach
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RAWFILL approach
Principle 1:combine complementary geophysical methods
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RAWFILL approach
Low resistivity+
High chargeability
Metals?
Resistivity model
Chargeability model
Principle 1: combine complementary geophysical methods
→ Increased certainty
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RAWFILL approach
Targeted sampling in
the zones of interest
revealed by
geophysics
Principle 2: targeted sampling
• Lower costs
• Reduced risk of
damaging
structures
• Reduced risks of
contamination or
exposure to
hazardous materials
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Pros and cons
• Non to minimally invasive
• Relatively low cost
• Large coverage
• See through technology
• Indirect information
• Resolution decreases with depth
• Prone to modeling errors
(artefacts)
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Proposed workflow
Archives & inventory report
• Gather and summarize all available information→ Build conceptual model→ Assess knowledge gaps
Geophysical characterization
• Use complementary geophysical methods planned according to the conceptual model→ Interpretation of geophysical results and detection changing properties
Calibration & validation
• Targeted sampling→ Build sampling plan according to geophysical results→ Verify and calibrate geophysical measurements to refine conceptual model
Resource model construction
• Build a resource distribution model based on refined conceptual model
Ad
dit
ion
al
mea
sure
men
ts r
equ
ired
?
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Proposed workflow
Landfill site
Potential knowledge gaps
Type of waste?Volume / Extent of the waste?Cover material?Contamination?
Initial stage
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Proposed workflow
Gather and summarize all available information
• Historical reports (from site owner, local authorities,…)• Aerial photography archives• Previous investigations
• Site visit• Information exchange • Discussing knowns and unknowns of the site
➢ Building conceptual model➢ Assessing knowledge gaps
1 Archives and inventory report
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Proposed workflow
Initial stage After gathering informationand visiting the site
1 Archives and inventory report
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Proposed workflow
Gathering and interpreting a priori information
First conceptual model
1 Archives and inventory report
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Proposed workflow
➢ Filling the knowledge gaps➢ Using non-invasive integrated approach
2 Geophysical characterisation
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Proposed workflow
Mapping techniques
2 Geophysical characterisation
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Proposed workflow
Geophysical imaging (here ERT/IP)
Profiling techniques
2 Geophysical characterisation
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Methods tested within RAWFILL
Method Bulk (geo)physical property
Relevant information for landfill characterisation
Sensitive to
Electrical resistivity tomography (ERT) or DC electrical resistivity
Electrical resistivity Cover layer thickness, waste zonation, leachate content, geology, groundwater table
Leachate contentClay contentMetal contentPore fluid conductivity
Induced polarization (IP) Chargeability Cover layer thickness, vertical extent, waste zonation
Metals, organics, wood, plastics
Ground Penetrating Radar (GPR)
Dielectric permittivity Electrical resistivity
Cover layer thicknessUtilities
Pore fluid conductivityClay and metal contentVoids
Electromagnetic induction (EMI)
Electrical conductivity and magnetic susceptibility
Lateral extentUtilitiesWaste zonation
Leachate contentPore fluid conductivityMetal content
Magnetometry (MAG) Magnetic susceptibility
Lateral extent, utilities, waste zonation
Metallic itemsMetal content
Seismics (refraction – SRT, surface waves - MASW, ambient noise – HVSNR or HV)
Elastic properties, density (seismic velocities)
Vertical extent, Geology StiffnessCompactionImpedance contrasts
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Methods tested within RAWFILL
Method Bulk (geo)physical property
Relevant information Acquisition/(ex. of main limitations)
Electrical resistivity tomography (ERT) or DC electrical resistivity
Electrical resistivity Water content, salinity, pore fluid, temperature, porosity, lithology
Borehole, cross-hole, surface/(impermeable membrane)
Induced polarization (IP) Chargeability Disseminated metallic particles (pyrite), clay, surface area, lithology
Borehole, cross-hole, surface (noise and inductive coupling)
Ground Penetrating Radar (GPR)
Dielectrical constant and electrical conductivity
Structures, faults, water content, salinity, pore fluid, porosity, lithology
Borehole, cross-hole, surface/(conductive ground)
Electromagnetic induction (EM)
Electrical conductivity and magnetic susceptibility
Water content, salinity, pore fluid, porosity, lithology, Ferrous materials
Borehole, cross-hole, surface, airborne or ATV mounted/(Metallic external objects)
Magnetometry (MAG) Magnetic susceptibility Ferrous materials (buried drums, containers…), lithology
Surface/(Metallic external objects)
Seismics (refraction – SRT, surface waves - MASW, ambient noise – HVSNR or HV)
Elastic moduli, density(seismic velocities)
Structures, faults, depth to bedrock, lithology
Surface, borehole, cross-hole/(velocity inversion, ambient vibrations)
Integrated approach:
• Using a combination of differentgeophysical methods
• Designed based on the a-prioriinformation available for a specific
landfill
Updated conceptual site model
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Proposed workflow
??
Use calibrated geophysical results for filling “gaps”
3 Targeted sampling to calibrate geophysics
Plan based on geophysical
results
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Electrical conductivity (EMI)
Low conductivity anomaly/background
High conductivity anomaly
Pipe:avoid utilities !!!
Knowledge gaps(e.g. depth calibration)
Anomaly other method
How to create a sampling plan?
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Proposed workflow
??
Final conceptual site model
Conclude all information into resource distribution model
✓ ✓
→ Information about volumes & feasibilityResource distribution model
4 Final conceptual site model
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• Location: UK, near Bristol
• Excavated for new housing in 2019
Case study: Emersons Green
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• Location: UK, near Bristol
• Excavated for new housing in 2019
→ ground truth data to calibrate
geophysics
Case study: Emersons Green
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Landfill size: 23,000m2
Depth: 3 - 5m
Operation (1984 – 1991)
• Inert & industrial/commercial waste
• Dilute & disperse basis
Step 1) Information gathering: site
historyArchives &
inventory report
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Step 1) Information gathering:
available ground truth dataArchives &
inventory report
Ground truth data available across site:
• 35 Trial pits
• 4 Boreholes
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Step 1: Identification of knowledge
gapsArchives &
inventory report
1. Waste thickness under defined especially
towards centre of landfill.
→ difficult to estimate waste volume
2. Structure of landfill unclear.
Is the landfill separated into different cells with different types of waste?
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Step 2) Geophysical characterisation: PlanningArchives & inventory report
Site conditions
Geophysical characterization
delineate extent & areas with high
leachate or metal contentdelineate extent & metallic materials
Top soil stripped off (about 30cm) In some places waste visible High groundwater table
→ Site well accessible for all geophysical measurements
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Step 2) Geophysical characterisation: PlanningArchives & inventory report
Selecting methods
Geophysical characterization
Lateral extent & areas with high
leachate or metal contentLateral extent & metallic materials
Electromagnetics Magnetics
MA
PP
ING
METH
OD
SP
RO
FIL
ING
METH
OD
S
MASW
Layers of different stiffness
Thickness of landfillWaste types & saturation
Thickness of landfill
ERT/IP
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Step 2) Geophysical characterisation:
Measurement extentArchives &
inventory report
Geophysical characterization
Magnetics EM: depths: 1.5m, 2.5m, 3m, 6m ERT and MASW
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Step 2) Geophysical characterisation:
Results Magnetics
Archives & inventory report
Geophysical characterization
Total magnetic field (nT) Vertical magnetic Gradient (nT)
Higher metalcontent?
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Step 2) Geophysical characterisation:
Results EM
Archives & inventory report
Geophysical characterization Cell type
structure?
Additional cell with less metal
content or thicker cover layer?
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Step 2) Geophysical characterisation:
Results ERT and IP
Archives & inventory report
Geophysical characterization
ERT
IP
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Step 2) Geophysical characterisation:
Results MASW
Archives & inventory report
Geophysical characterization
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Step 3) Calibration and ValidationArchives & inventory report
Geophysical characterization
Calibration & validation
Additional ground truth data through excavations
base of waste layer
cover layer thickness
clay stank dividing the waste cells
• The landfill was separated into three cells. These cells were
excavated into the natural clayey ground and filled with waste.
• A thicker clay cap and a thinner waste layer was found in cell 3.
• A step in the landfill base between cells 2 and 3 might be
associated with the underlying sandstone.
• The waste composition was a mix of
plastic, metal, wood, paper, fabric, inert
etc. with no strong compositional
changes across the site.
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Step 3) Calibration and ValidationArchives & inventory report
Geophysical characterization
Calibration & validation
EM: good delineation of waste cell extent and cover layer thickness
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Step 3) Calibration and ValidationArchives & inventory report
Geophysical characterization
Calibration & validation
IPresolves clay cap
and waste cells
ERTresolves
sandstone
interface
MASWresolves sandstone
interface, mudstone
interface less clear
cover layer
mudstone sandstone
waste cell 2waste cell 1waste cell 3
sandstonemudstone
inert waste?
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Step 4) Building Resource Distribution ModelArchives & inventory report
Geophysical characterization
Calibration & validation
Resource model construction
Trial pits & boreholes
Geophysical data
Correlation analysis
extract geophysicaldata in vicinityof samples
choice of relevantgeophysicalparameters
discretize sampling logs into relevantcategories (e.g. clay cap, saturated waste…)
Model buildingthrough supervised machine learning
(classification)
Cell 01 (North) Cell 02 (centre) Cell 03 (South) Total
Volume of waste
material (m3)15’258 10’654 9’547 35’450
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• Using geophysics:
• is cost effective
• allows targeted sampling
• delivers relatively high resolution data (when mapping and profiling techniques are combined)
• Our proposed workflow:
• integrates a priori information, geophysics and targeted sampling to build a resource distribution model specific to each landfill
• Provides “ready-to-use” information for decision makers (DST 2)
Take-home message
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The Interreg North-West Europe Project is coordinated by SPAQuE and
unites 8 partners from 4 EU regions.
Raw materials recovered from
landfills